I don’t think a trinity system would be bad, as long as they do it right; Any class could potentially do everything as is, and they could still develop around that for trinity by adding tree buffs for roles, just as the example people have used for druids from WoW (Since they can heal, tank, magic dd, or melee dd).
I think it would be more of a hopeful wish than anything though, since they would have to redevelop every class and the combat mechanics for every class/dungeon/mob/boss, which could take a long time.